I just did a compression test on my USDM B18C5 motor with Skunk2 cams and Toda cam gears. Here are the results

220, 220, 205, 215

Are these results ok? Cylinder 3 took more than the standard 5 cranks to get it to 205 but it kept increasing with every crank until a total of 8 cranks. Does the cam gear setting affect the numbers?

If these results are fine I may try and put a thin head gasket in to raise the compression a bit.

Thanks,

AW

 

Numbers look good to me... Mine were in that neighborhood.

 

 

if #3 took a little longer to get there (and didn't quite make it), then it may be getting a little weak, but no biggy

d

 

What would the cr (approx.) for 255psi?

I noticed that most stock itr's push out about 210-225psi.

 

try it again.. and do it with a full open throttle.... there should be quite a big difference..

 

Unfortunately, this was performed with the throttle pressed to the floor.

AW

 

you can try put some motor oil in there and wet test again!
not bad now!

 

you're ok. I'm putting out 230 lb psi on 11.5:1 with 40K miles.

 

So.. It seems a general "rule of thumb" for figuring an approximate target psi for a compression test would be to double the C/R and multiply X 10?
Example: 11.1 C/R X 2 = 22.2 X 10 = 222 psi?
255psi ÷ 10 = 25.5 ÷ 2 = 12.5:1 C/R?
Just throwing out ideas. Totally guessing. :-)

 

There's a difference between static CR and dynamic CR, since you can change the dynamic CR very easily (cam gears for example) there is no formula to convert to static CR. You do calculate static CR, but the dynamic CR doesn't play a role in the calculation.

As for the OPs numbers, they are fine. Different gauges will give slightly difference readings, adding oil will give a different (but useless except for some minor troubleshooting) reading. Keep the fuel pump off and the throttle wide open.

 

2001 b18c5 here 220 on all 4

 

Not bad, My buddy just did a test on his B16 with bolt on's and CTR intake cam. 240 across.

When's the last time you adjusted your valves? That helps too.